With any internal combustion engine it is desirable to treat the exhaust gases so that they can be safely discharged into the atmosphere. In some engines, particularly the diesel type, among the most prevalent operating problems is the presence of particulates which are carried in the exhaust gas stream.
Primarily, the particulates are normally bits of carbon. They result from the incomplete combustion of the hydrocarbon fluid under certain engine operating conditions. However, the operating efficiency of the engine is also a contributing factor to the amount of carbon produced.
The presence of relatively large amounts of carbon particles in any exhaust gas stream may be evidenced by a dark, smoky, undesirable effluent. Such smoke is not only offensive aesthetically; in large quantities it can be unhealthy.
Means have been provided and are known to the prior art for elimination or minimization of the particulate content in exhaust discharge streams. However, it has been found that while the particulates can be minimized by a suitable filter of proper construction, eventually it can become saturated and/or inoperable due to excessive particulate accumulations.
It is further known that the overall engine exhaust gas treating process can be expedited. This is achieved not only by passing the gas stream through a filter medium, but by providing the filter with a catalyst which will promote oxidation of certain constituents present in the exhaust gas stream.
It should be appreciated that the generation of carbon particles is prevalent under all diesel engine operating conditions. It is further appreciated that the quantity and quality of an exhaust gas stream created in any internal combustion engine will vary in accordance with the operating characteristics of the engine.
For example, the temperature range experienced by the diesel exhaust gas stream can vary between slightly above ambient air temperature, and temperatures in excess of 1200.degree. F. When the exhaust gas is hot enough, the carbon particles trapped in a filter will be combusted. However, the engine operating conditions where this rejuvenation can occur is seldom reached in diesel passenger cars.
Where it is found that an engine continuously operates under such circumstances that the particulates are continuously produced and accumulated in the filter, the particulate trapping filter bed must be occasionally rejuvenated.
Under usual circumstances, rejuvenation will consist of merely introducing the hot exhaust gas stream, containing sufficient oxygen, into the filter bed to contact and ignite or incinerate the refined carbon particles. The combustion of any large and contained carbon accumulation can, however, produce temperatures greatly in excess of that of the exhaust gas. The result is that at such excessive temperatures, the filter bed or element is susceptible to thermal shock, damage or distortion.
Toward achieving a satisfactory or limited rate of carbon removal from an exhaust gas system without incurring resulting damage to the filter, the unit presently disclosed is provided.
The instant apparatus thus comprises in brief, a pretreating chamber which contains a catalyst bed through which at least a portion of the exhaust gas stream is passed. This catalyst bed is disposed at a point upstream of, and spaced from the main filter bed.
To assure that the main or primary filter bed or beds always remain functional, the exhaust gas stream is periodically and regularly heated. It is thus brought to a temperature in excess of the temperature required to initiate combustion of retained particles. This step will preclude the build-up of any appreciable amount of combustibles.
The main filter bed, or beds when a plurality of the latter are used, will thus be regularly and at periodic intervals, rejuvenated. Such treatment, if repeated at predetermined intervals, will preclude any carbon accumulation which might otherwise lead to thermal stress or damage to the bed.
It is therefore an object of the invention to provide a filter system of the type disclosed which is capable of containing combustible particles from an exhaust gas stream, and subsequently being periodically rejuvenated by burning said particles.
A further object is to provide a particular filter of the type disclosed which is capable of removing solid elements from an exhaust gas stream while permitting periodic rejuvenation of the filter element while the engine is operating at conditions that would normally result in a relatively cool exhaust gas temperature.
A still further object is to provide an exhaust gas treating system which is capable of removing particulates from an exhaust gas stream without jeopardizing the integrity of the filter bed.